1. Field of Invention
The present invention relates to a voltage regulator for an alternating current generator, and more particularly to a control apparatus for controlling a generating voltage of a generator for an automotive vehicle and for charging a battery mounted on the vehicle.
2. Brief Description of Prior Art
In a conventional voltage regulator of this kind, a generating voltage of an alternating current generator is maintained at a constant value by controlling a field current for the generator irrespective of a rotational speed of the generator and an increase or decrease of electrical loads.
When a large electrical load, such as head lamps of an automotive vehicle or the like, is used in a range of a low speed running operation of the generator, a field current for a field winding is rapidly increased by the voltage regulator until the generating voltage reaches a predetermined value. And unless the generating voltage reaches this value, the field current is increased to its maximum value. In a generally-known alternating current generator, in particular, in a generator wherein a field current is branched off from a battery charging line and supplied to the field winding, an effective battery charging current is rather decreased even if the field current is further increased after the field current exceeds a predetermined value, since the effective charging current is obtained by subtracting the field current from a generated current at the generator.
According to the observations of the present inventors, it was found out that a maximum field current by which a maximum effective charging current is obtained depends on a rotational speed of the generator and is increased in response to the increase of the rotational speed of the generator. This will be further discussed in the following description.
According to the above observations, it is useless to increase the field current above a predetermined value, since to do so may cause a problem in that a power transistor of the voltage regulator for controlling a supply of the field current may be unnecessarily heated.